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World record for high-temperature fuel cells

Jülich researchers make a promising energy technology even more effective

[9. Juni 2004]

Scientists from Research Centre Jülich have set a new record performance. Using hydrogen as fuel gas, a solid oxide fuel cell stack (SOFC) consisting of 60 single planar - flat - cells delivered a power of 13.3 kilowatts. This would be enough to supply a small apartment building with electricity at periods of peak demand. The mean operating temperature was just 760 degrees Celsius - a relatively low temperature for solid-oxide fuel cells, which has a favourable effect on the life expectancy of the materials used.

Fuel cells achieve especially high efficiencies in producing electricity and heat from fuels like hydrogen and natural gas. Hydrogen operation completely avoids emission of the greenhouse gas carbon dioxide, and in the case of natural gas such emissions are considerably lower than for instance with boilers and internal combustion engines. Solid oxide fuel cells (SOFCs) are the hot favourites for future application in buildings, power stations and motor vehicles.

At Research Centre Jülich, scientists are developing SOFCs characterized by a thin electrolyte and planar single cells. Researchers from the Jülich Institute for Materials and Processes in Energy Systems (IWV) and the Central Department of Technology (ZAT) have now connected 60 such cells to form a stack, which they operate at a temperature of around 800 degrees Celsius. The stack, roughly 40 centimetres in height, supplied a power of 13,300 watts. This research is supported, amongst others, by the Federal Ministry of Economics and Labour and also by EU project funds.

Due to the prevailing temperature, methane as a fuel is directly converted into hydrogen and carbon dioxide in the stack - an advantage for SOFCs in comparison to other types of fuel cells operating at lower temperatures. This feature makes the SOFC especially efficient. Furthermore, the effort required in processing natural gas fuel, which mainly consists of methane, can be kept to a minimum. This reduces the cost of the entire fuel cell system and, moreover, enables it to be used in vehicles for on-board electricity generation. With such a methane-hydrogen mixture, the stack still reached a power of 11,900 watts.

The Jülich fuel cell stack has now been in continuous operation for more than 1100 hours. During this period, it has only lost about three percent of its power. "This loss can be attributed to the behaviour of individual stack layers rather than to "ageing" of the stack as a whole", explains Dr Robert Steinberger-Wilckens, head of the fuel cell project at Research Centre Jülich.

SOFC world records are almost a tradition at Jülich. This is the third time that scientists from the fuel cell project have reported a top performance. About two years ago they achieved 9.2 kilowatts in hydrogen operation with 40 single cells. "It would be quite wrong to attribute the present increase in performance to 13.3 kilowatts merely to increasing the number of cells from 40 to 60", Steinberger-Wilckens comments. The present record was actually achieved at temperatures more than 100°C lower, thus demonstrating that the use of improved SOFC cells significantly reduces the operating temperature whilst attaining the same power output. The lower temperature results in a longer lifetime for the stack. This progress was also in part due to improvements in joining techniques and the new steel "JS-3" specially developed at Jülich.

A stationary power supply requires operating times of more than 40,000 hours, whereas 5000 to 10,000 hours are sufficient for use in motor vehicles. "We have come a good bit closer to achieving these operating times", Steinberger-Wilckens is pleased to report.

The new fuel cell stack (above) consists of 60 single planar cells (below) and supplies a power of 13.3 kilowatts - a new world record!